An estimated 6 million women in the US suffer from vulvodynia. Provoked vestibulodynia, which typically is associated with vulvar vestibulitis, occurs most often in premenopausal women. This chronic pain syndrome is characterized by increased numbers of nociceptor axons usually localized to the posterior vestibule. Clinical evidence suggests that reproductive hormones influence the development and severity of vulvar vestibulitis syndrome (VVS). Aside from surgical excision of the hyperinnervated tissue, there are no effective therapies. This application proposes preclinical studies designed to characterize an animal model of VVS, and to use it to assess biological mechanisms that may be amenable to therapeutic targeting. We developed a rat model of VVS that replicates many clinical findings in humans. Small-volume injections of complete Freund's adjuvant into the rat posterior vestibule evoke persistent hypersensitivity and hyperinnervation. In Aim1, we use this model to investigate neural consequences of vestibular inflammation, including sprouting and phenotype alterations. We will investigate the persistence of hyperinnervation and its correlation to mechanical vestibular sensitivity, and determine if our model shows behavior consistent with dyspareunia. We will assess whether estrogen, which alters normal patterns of nociceptor innervation, also affects development of hyperinnervation. We will build on preliminary findings that progesterone administered to juvenile rats causes persistent increases in sensory innervation density, and determine whether this augments development of vestibular hyperinnervation. We will assess the extent to which our model simulates human cytological changes by comparing findings in rats with tissue excised from patients with VVS. In Aim 2, we test the hypothesis that activation of the angiotensin II receptor type 2 (AT2) mediates hyperinnervation and hypersensitivity in VVS. In preliminary studies, we show that AT2 blockade abrogates hyperinnervation and hypersensitivity in our model. We hypothesize that inflammatory cells create a local renin-angiotensin system that synthesizes angiotensin II, which initiates sensory axon sprouting. We will determine if angiotensin II is synthesized by rat and human vestibular tissue, and using explant cultures, that it elicits sprouting. We will determine i AT2 activation in the absence of inflammation elicits sprouting and hypersensitivity in our rat model. We will determine if AT2 antagonism not only prevents, but also reverses hyperinnervation and hypersensitivity. We will determine if AT2 blockade is overcomes hyperinnervation and mechanical sensitivity augmented by the actions of reproductive hormones. This application will provide fundamental information on mechanisms that regulate innervation in normal and inflamed vestibular tissue. It employs a novel rat model to identify the biological underpinnings of vestibular inflammatory hypersensitivity with the intention of manipulating a key signaling pathway in order to identify new therapeutic targets in VVS. Information obtained in these studies has strong potential to substantively change our thinking and clinical approach to the management of some forms of vulvodynia.